Conventionally, there has been known a projector-type vehicle lamp which is configured to irradiate light from a light source disposed at the rear of a projection lens through the projection lens to the front.
In a vehicle lamp disclosed in Patent Document 1, a projection lens is configured by two lenses disposed on an optical axis extending in a vehicle longitudinal direction.    Patent Document 1: Japanese Patent Laid-Open Publication No. 2014-26741
In a vehicle lamp such as a headlamp, it is desirable to form a light distribution pattern in which light unevenness is as small as possible, as a light distribution pattern to be formed by the light irradiated.
In a conventional projector-type vehicle lamp, a plano-convex aspherical lens whose front surface is configured as a convex curved surface is often used as a projection lens. However, a large coma aberration occurs in the projection lens having such a configuration. At that time, a tail of the coma in the coma aberration extends inwardly (i.e., toward an optical axis) in an optical image forming system where light is incident on the projection lens from the front.
On the other hand, when such a projection lens is used in an illumination optical system, blurring due to the coma aberration occurs. The blurring is formed in such a way that the tail of the coma extends toward the outside of a light distribution pattern. Therefore, a light distribution pattern to be formed by the light irradiated from a vehicle lamp having such a projection lens is formed such that an outer peripheral edge portion gradually becomes darker. As a result, the uniformity of the light distribution pattern can be enhanced.
By the way, when the projection lens is configured by a plurality of lenses, a thickness of each lens can be thinned. Therefore, it is possible to effectively suppress the occurrence of sink marks even when employing a resin lens or the like.
Even when the projection lens is configured by a plurality of lenses in this way, in order to enhance the uniformity of the light distribution pattern, it is desirable to form the light distribution pattern in which the blurring due to the coma aberration occurs in such a way that the tail of the coma extends toward the outside of the light distribution pattern.